In the manufacture of color cathode ray tubes (CRTs) for the visual displays in television receivers and computers, it is becoming increasingly more important to permanently identify the CRT faceplate. A color cathode ray tube includes a plurality of components including a faceplate with a grille and phosphor screen on its rear surface, a mask with apertures which correspond to the pattern of phosphor dots or lines on the screen, a funnel attached to the faceplate as well as to a neck which supports an electron gun, and a yoke for deflecting the electron beams.
The coding of the faceplate would enable the manufacturer to determine the source of defects and to more easily correct them. For example, it would permit a determination of which machine in the process caused the defects, assuming that the code is also monitored at the machine that caused the defect. These machines would include, for example, the gun sealing station for sealing the gun to the neck, the lighthouse for producing the phosphor dots or lines forming the screen on the rear of the faceplate, the grille machine for applying the grille to the rear of the faceplate, the mask welding machine for welding the mask to the rails in the case of tubes using flat tension mask technology, and a plurality of others.
It would also be desirable to code the masks as well as the faceplates to permit the masks to be separated from the faceplates during manufacture and rejoined at some later step in the manufacturing process without fear of joining the wrong mask to a given faceplate.
As is well known, present commercial CRT technology mandates the dedication of a particular mask to a particular faceplate because the dedicated mask is utilized to generate the phosphor pattern on the faceplate and thus cannot be interchanged. By encoding both the faceplate and the mask, it would be possible to separate them at will during manufacture and to later rejoin them properly.
However, it has heretofore not been commercially practical to code the faceplate because known coding techniques cannot withstand the kiln temperature, on the order of 460 degrees C., required to join the funnel to the faceplate. Conventional coding techniques such as paint spraying or printing methods simply will not hold up at these high kiln temperatures. Also, various acids and caustic wash processes are used that could destroy conventional labels.
It is a primary object of the present invention to provide a method for permanently applying a bar code to CRT faceplates that withstands the rigors of the manufacturing process.
In accordance with the present invention a method of manufacturing CRT tubes with binary coded faceplates is provided including dispensing a frit paste on the faceplate in the form of a bar code. While a USS-1 2/5 bar code is illustrated herein, any other bar code such as Code 39, U. P. C., etc., can be applied by this process. The frit is devitrified as part of the conventional faceplate processing either during faceplate normalization or during devitrification of the mask rail frit in flat tension mask technology without any separate step of devitrifying the code.
In one embodiment of the present invention, frit is dispensed through a single dispensing nozzle and the nozzle is moved relative to the faceplate along x and y coordinates to form a single undulating line. Parallel line portions of this undulating line define the code itself and the lines are joined at their ends by generally semi-circular line portions. By utilizing curved line portions as opposed to sharp 90 degree turns at the ends and beginnings of the parallel line portions, considerable time saving is accomplished because the nozzle takes less time to complete these curved line portions than if if followed a rectangular path.
The narrow bars of the 2/5 bar code are formed by a single pass of the nozzle, while the wide bars are formed with a triple nozzle pass.
An important aspect of the present invention is that the code is formed as a negative image to both conserve dispense time and frit because it is then unnecessary to dispense frit in the "quite zone".
In another embodiment of the present invention, frit is selectively dispensed through a plurality of nozzles numbering 18 for each character pair, and 2 start-up and 4 stop bar nozzles, plus 10 nozzles for each of 2 quiet zones if a positive code image is desired.
In both embodiments, however, frit flow is a constant volume flow, produced through the application of pressure. Frit flow is terminated, not by valving the frit paste, but instead by the application of a high negative pressure to the frit at the dispensing nozzle and then a low negative pressure. The switching of these pressures is accomplished with solenoid operated valves. Also in both embodiments, a predetermined distance is maintained between the faceplate and the nozzle tip by a follower stylus carried by a dispensing head and nozzle assembly. The nozzle tip thus follows any curvature of the faceplate.
On curved faceplates, the bar code is usually located on the outer surface of the peripheral faceplate integral flange while in the flat tension mask technology, the bar code would typically be located at a predetermined location on the front face of the panel its edge.
Through the use of the present coding method, it now becomes possible, with code sensing at all stations during the manufacturing process, to identify and isolate a particular machine causing defects in a simple and efficient manner thereby providing far superior quality control than heretofore known in CRT manufacturing technology.
The present faceplate coding technique, when utilized in conjunction with a mask code, permits separate random movement of the faceplate and mask when desired through portions of the manufacturing process and then enables them to be properly remated prior to final assembly. That is, by sensing both faceplate code and mask code at a joining location, the proper mask will be joined to the proper faceplate. This is an extremely important capability in CRT technology today where the mask is dedicated to a specific faceplate through the manufacturing process even though not physically permanently joined together.
Other objects and advantages of the present invention will appear more clearly from the following detailed description.